Karyotyping Lab
Aneuploidy is a change in the number of chromosomes that can lead to a chromosomal abnormality. In
humans, in every cell of our bodies, we typically will have 23 pairs of chromosomes. From each pair, we
typically will inherit one chromosome from our mother and one from our father. The first 22 pairs of
chromosomes are referred to as autoscores, or body chromosomes. They are numbered from 1 through
22 from largest to smallest. The last pair of chromosomes are the sex chromosomes. Females will
typically have two X chromosomes, while males will typically have one X chromosome and one Y
chromosome.
Every so often, during meiosis, gametes may form in which the chromosomes do not separate correctly,
leading to sperm or egg cells carrying too many (n + 1) or too few (n – 1) chromosomes. This failure to
separate is called NONDISJUNCTION. If this gamete fertilizes/is fertilized, the zygote that develops will
inherit too many/too few chromosomes. This condition will be copied into every successive cell of the
embryo.
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A monosomy refers to the presence of only one chromosome (instead of the typical two in
humans) from a pair.
A trisomy is the presence of three copies, instead of the normal two, of a particular
chromosome. The presence of an extra chromosome 21, which is found in Down syndrome, is
called trisomy 21.
A translocation is a chromosome abnormality caused by rearrangement of parts between
nonhomologous chromosomes.
DIRECTIONS:
Cut out the chromosomes from the picture plate you were given by your instructor. Pair them up
according to size, banding pattern and centromere position. Lay them out in descending size order and
according to the centromere positions as stated on the front page of instructions (Groups A thru G).
Save the sex chromosomes for last!
When you are sure you have them arranged correctly, glue them down on the grid provided. At the
bottom of the paper, be sure to write the chromosome #, the sex of the subject, and the abnormality
present (if any). If no abnormality is detected, write “normal”. You MUST write NUMBER of the
chromosome smear you are analyzing on the completed karyotype for full credit!
POST-LAB questions. These can be answered beneath each question.
1.
How many chromosomes are normally present in a human muscle cell? In a human zygote? In
a human eggs cell?
2.
How does an autosome differ from a sex chromosome?
Karyotyping Lab
3. In making a karyotype, what are three characteristics of the chromosomes that can be used to
pair homologues?
4. What is “nondisjunction”? How does nondisjunction occur? What is the result of a
nondisjunction?
5.
What was the sex of the person in the karyotype that you constructed? How can you tell?
6.
Aside from the sex of the subject, what else did you learn from the karyotype you constructed?
7. Summarize the genetic condition you found in the karyotype you analyzed. What are some of
the expected symptoms of this disorder? Life expectancy? What are the odds of this condition
occurring in the general population? Use your textbook or an internet source (citation
needed!)
8. In your own words, what is the value of prenatal genetic screening, such as karyotyping?
Karyotyping Lab
9.
What are some drawbacks of genetic screening (in general), or karyotyping (specifically)?
10. What genetic information does a karyotype NOT tell you about an individual?
Discussion Questions (multi-part short essays). Attach a separate paper with your answers.
11. What special problems arise with a genetic disease that does not show up until age 40?
12. A genetic disease can be completely eradicated if the people who have the disease or carry the gene
do not have children. How do you feel about this? List the pros and cons in your answer.
13. If a test could be done to show if you were a carrier of a particular dominant gene that causes a
disease that does not manifest itself until age 40 and it has been known to run in your family, would you
have the test done? Why or why not? Should a person be required to have such a test? List some pros
and cons of your answer.
14. Several genetic disorders can be detected before birth. What are two tests that can be done? In
New Jersey, any women over the age of 35 is required to have a prenatal test done or sign a waiver that
she absolves anyone of responsibility. Why does this apply to women of such an age? Should these
tests be required? Who should pay for the care and medical costs of children born with these
abnormalities? List pros and cons in your answer.
15. Name a genetic disease that is associated with a particular ethnic group and some characteristics of
that disease. Suppose that there was a good chance that such a gene was in your family history. Would
you see a genetic counselor about it? What would you do with the information received?